When my daily reading takes me into the Old Testament Law, I always ask God to show me how to apply it to my life now. We aren't called to live by the Law. We are called to live by Grace (check out Romans 8 on that subject), but the Law can still teach us stuff that does apply to our modern lives.
Leprosy is still a real disease, but let's look at it in a spiritual way. You could look at sin as a spiritual leprosy, a disease that spreads, a spiritual sickness that will infect all it touches. And every sin has this potential, even a little one, like a white lie (as we call them today) or a silence when we should have spoken, or a time you lost your temper and justified it. These aren't "huge" sins if we compare them to other sins, but this comparison thing isn't what God ever does. It gives us no truth. It doesn't help us. It isolates us from others for when we compare ourselves to others either we look better or they look better, and our eyes are on people rather than God.
I want to share with you is a blog about biblical leprosy written by a biology professor, Dr. Alan Gillen. He has some good quotes (beware if you go there -- there a photograph of leprosy that isn't pretty).
Let me share from this article (which is found at http://www.answersingenesis.org/articles/am/v2/n3/the-disease-that-shuns):
biblical leprosy is a powerful symbol reminding us of sin’s spread and its horrible consequences. Like leprosy, sin starts out small but can then spread, leading to other sins and causing great damage to our relationship with God and others.
Exactly! But there is hope. Gillen also writes:
Jesus freely touched people with leprosy. While people with leprosy traditionally suffered banishment from family and neighbors, Jesus broke from the tradition. He treated lepers with compassion, touching and healing them.
Jesus is still the same today. He comes to us in our time of our need, our brokenness and will restore us if we want to restored.
Don't let sin stay in your life. Fall at Jesus' feet. Ask for cleansing. And He will do it. And you will be free.